Fair Value Of Assets And Liabilities (Tri-Level Hierarchy, Carrying Value) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	$ 255.9us-gaap_AvailableForSaleSecurities	$ 244.1us-gaap_AvailableForSaleSecurities
Assets held for policyholders	1,697.9us-gaap_OtherAssetsFairValueDisclosure	1,416.0us-gaap_OtherAssetsFairValueDisclosure
Total	2,691.9us-gaap_AssetsFairValueDisclosure	2,360.9us-gaap_AssetsFairValueDisclosure
Total	(1.4)us-gaap_LiabilitiesFairValueDisclosure	(2.0)us-gaap_LiabilitiesFairValueDisclosure
Foreign time deposits	29.6ivz_ForeignTimeDeposits	28.8ivz_ForeignTimeDeposits
Equity method investments	332.1us-gaap_EquityMethodInvestments	308.2us-gaap_EquityMethodInvestments
Cost method investments	4.6us-gaap_CostMethodInvestments	5.6us-gaap_CostMethodInvestments
Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equities	(1.4)	(1.7)
Note Payable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note payable		(0.3)
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	474.9	447.8
Seed Money [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	246.2	233.8
Trading investments	68.2
Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	3.4	4.0
Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	6.3	6.3
Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	162.6	249.7
Common Shares [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	29.0
Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	1.4	2.1
UIT-Related Equity And Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	1.6	1.2
Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0.4
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	1,697.9	1,416.0
Total	2,681.8	2,350.6
Total	(1.4)	(1.7)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equities	(1.4)	(1.7)
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Note Payable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note payable		0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	474.9	447.8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Seed Money [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	246.2	233.8
Trading investments	68.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	162.6	249.7
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Common Shares [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	29.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	1.4	2.1
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| UIT-Related Equity And Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	1.6	1.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	0	0
Total	0.4	0
Total	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equities	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Note Payable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note payable		0
Significant Other Observable Inputs (Level 2) [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Seed Money [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Trading investments	0
Significant Other Observable Inputs (Level 2) [Member] \| Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Common Shares [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Significant Other Observable Inputs (Level 2) [Member] \| UIT-Related Equity And Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Significant Other Observable Inputs (Level 2) [Member] \| Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0.4
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held for policyholders	0	0
Total	9.7	10.3
Total	0	(0.3)
Fair Value, Inputs, Level 3 [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate equities	0	0
Fair Value, Inputs, Level 3 [Member] \| Note Payable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Note payable		(0.3)
Fair Value, Inputs, Level 3 [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] \| Seed Money [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	0	0
Trading investments	0
Fair Value, Inputs, Level 3 [Member] \| Collateralized Loan Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	3.4	4.0
Fair Value, Inputs, Level 3 [Member] \| Other Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale investments	6.3	6.3
Fair Value, Inputs, Level 3 [Member] \| Deferred Compensation Arrangements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Fair Value, Inputs, Level 3 [Member] \| Common Shares [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0
Fair Value, Inputs, Level 3 [Member] \| Corporate Equities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Fair Value, Inputs, Level 3 [Member] \| UIT-Related Equity And Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	0	0
Fair Value, Inputs, Level 3 [Member] \| Municipal Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading investments	$ 0

Corporate Equities

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- Definition

Any certificate of deposit or savings account held by a bank or other financial institution for a specified period of time. These Foreign time deposits are of a large denomination, have maturity dates of three months or longer, and are combined with marketable securities.

+ References

No definition available.

+ Details

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

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-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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- Definition

Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 50

-Paragraph 1

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-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=29638308&loc=d3e40346-111594

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Period Type:	instant

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

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